Inorganic fibers and method of preparation



is carried out.

3,082,099 INORGANHZ FIBERS AND NEETHOD OF PREPARATION Robert M. Beasleyand Herbert L. Johns, Cleveland, Ghio, assignors to Horizonsincorporated, Cleveiand, Ohio, a corporation of New liersey No Drawing.Filed Feb. 26, 1960, Ser. No. 11,121 9 Claims. (Cl. 1l5--39) Thisinvention relates to novel inorganic fibrous compositions, to methodsfor preparing same and to the formulations from which they are prepared.More particularly, it relates to the preparation of novel inorganicfibers possessing outstanding structural and mechanical properties, tothe fibers themselves and to their utility as insulation against heat orsound.

In an earlier filed United States patent application, Serial No.777,193, filed December 1, 1958, we have disclosed a procedure forforming inorganic fibers by removing the liquid phase from thin films ofsuitable composition disposed on surfaces to which the composition doesnot adhere. The application also discloses that the dimensions andproperties of the fibers so produced may be controlled by varying themanner in which the process Improvements of the process described in theaforesaid application are described in a related United States patentapplication, Serial No. 829,220, filed July 24, -1959.

In the aforementioned applications, the fiber-forming process isdescribed in terms of various fiber yielding compositions which includethe following: sols comprising either dispersions of inorganic oxides inwater solutions; or solutions of organic salts, particularly the metalsalts of organic acids exhibiting dissociation constants of at least 1.5x10- dissolved either in aqueous or non-aqueous solvents, either aloneor in admixture with one another.

It has now been found that by employing as the filmforming composition acomposition consisting of the following essential components in suitablerelative proportions (1) a water soluble metal salt of an organic acid,(2) a salt of a metal and a strong inorganic acid, and (3) a properlyconstituted silica sol, several important advantages accrue over theprocedures and products defined in the aforementioned earlier filedapplications.

In general terms, these advantages may be stated as follows:compositions having a much higher concentration of dissolved oxide(actually present as salts) may be used with greatly increased speed ofproduction of fibers, but without hindering the effectiveness of thefiber production. Further by the use of these compositions in a specificpH range, not only is this greatly increased speed of productionobtained but the fibers are generally smaller in cross section and ofgreater length than those obtained with the procedures disclosed in theearlier referred to applications. In addition, the fibers obtained fromsuch relatively higher speed production are superior in many mechanicalrespects such as strength, flexibility before and after firing,restriction on crystal growth, and general utility.

Novel fibers produced in accordance with the present invention are inthe form of ribbons of rectangular cross section in lengths ranging fromless than 1 up to 8" and having widths in the range of about 2 micronsto 20 3,08Z,fi9 Patented Mar. 19, 196

microns and thicknesses from about 0.1 to about 1 micron and consist oftwo classes of chemical compo: tions, one being a modification of theother: the fil class consists of between about 5% and 15% by Weig ofsilicon dioxide and between about 95% and of metal oxide; the secondclass consists of ratios of SillCl dioxide and metal oxide identicalwith the dCSCIlPtlt in the preceding phrases, but complexed further Wichemical combinations of water of hydration and residu carboxylic acid.The second class is produced at It temperatures of heat treatment andthe first class is o tained as the result of heating these low temperatuproduced materials to temperatures sufiicient to can sintering.

The elements which may be used for the major porti of these novel fibersmay be selected from the group co sisting of aluminum, the rare earths,zirconium, hafniui chromium, thorium, iron, cobalt, manganese, nickel a1vanadium. These are supplied to the fiber-forming cor position in theform of organic salts or as salts of stro inorganic acids or both.

The organic salts of these metals are those wherein tf acid isan'acyclic carboxylic acid Whose dissociation co stant is at least 1.5.10- Among the acids whose met salts may be used are the following:formic, acetic, oxal: maleic, adipic, itaconic, citric, tartaric, lacticand tilt halogen derivatives, e.g. chloroacetic acid, and the lil Ofthese we prefer the acetates because of their rea commercialavailability and their low cost when cor pared with the salts of theother acids stated above.

The inorganic acids whose metal salts have been fom particularlysuitable are HCl and HNO As in the ca of the organic salts, the saltsare preferably supplied the fiber-forming composition in the form of aconce trated water solution. Depending on the salt, such co centrationsmay vary from a minimum of 10% oxi content to as high as 35% oxidecontent dissolved the solution.

The fiber-forming composition may be formed of mi tures of more than twosalts. The composition compris a major proportion of a water solubleorganic salt a: a minor proportion of a water soluble inorganic satogether with a small amount of a properly constitut silica sol.

The addition of suitable amounts of silica sol to mi tures of organicand inorganic salts described above, 2 celerates the fiber-formingprocess and in addition it 11 been found that by control of the amountof silica the final product a fiber is produced which has grea strength,flexibility and mechanical integrity than produced in its absence.

The silica sol is preferably supplied to the compositi in concentratedform, for instance as concentrations from 30% to 50% of silica dispersedin water. The p1 portion of silica sol in the fiber-forming compositionsuch as will provide a total content of silica in the fit fiber varyingbetween a lower limit of 5% and an up; limit of 15% by weight.

Two distinct kinds of fibers are obtained as a res of processing ofthese compositions depending on the h treatment. In the first, involvingremoval of fibers f1( the smooth surface at temperatures not exceedingabc 200 C., the compositions are made available in 1 form of ribbon-likefilaments, and this structure is mai tined throughout subsequent heattreatment. In this rst low temperature phase the oxides and the mixturesiereof comprising the chemical makeup of the fiber still )ntainsignificant amounts of combined water, generally l the form of hydroxylgroups, and residues of carboxylic :id substituents. The mineral acidportions are pretty ioroughly dissipated. In this form they are stillchemiilly reactive towards strong acid reagents but are inluble inwater. In addition, they are porous, adsorptive, id in all probabilitycontain submicroscopic capillaries. lhen such fibers are fired to asintering temperature, lrinkage of about 30 to 35% takes place in thevarious imensions, the porosity is eliminated so as to yield a ensetranslucent to transparent structure, and the soluility in chemicalreagents is minimized or eliminated. The amount of organic hydratedmaterial which still :mains is a function not only of the metal oxideused, it also of the organic acid. For example, in the case E thezirconia fibers complexed with silica, the loss in eight between fibersas formed directly on the smooth irface and fibers after having beensubjected to sintering mperature is approximately 33 to 35%. Chemicallyit as been determined that the zirconia compound present l the fiberafter low temperature formation in the case here the acetate is used isin accordance with the empirill formula:

(CZHQOZ) [is being an empirical formula approximately equivalent about67% zirconium oxide by weight. In the case E the alumina acetatecompound, for example, the loss 1 weight between the 200 C. fiber andthe fiber after ntering empirically appears to be equivalent to theequa- The amount of organic substituent remaining with the her at atemperature not exceeding 200 C. is, to a cerin extent, a function ofthe boiling point or sublimation aim of the acid involved. Somedecompose to form tixed carbonates and hydrates. For example, oxalicacid roduces compositions comparable to those obtained from re acetatesin view of the fact that it sublimes at 150 whereas the citric acidderivatives produce darklored caramel type derivatives, but still infibrous forms. The low temperature fiber may be utilized in this form )rcomplexing purposes when it is desired to make intereavings of fiber ofone composition with another in order achieve directional properties asa function of chemical )mPOSltiOIl. Such complexing is moreadvantageously :complished at this stage rather than at a later stage.

It has been further found that the fibering process pro- :eds mostrapidly at highly acid pHs below 2 and preferly within the range of l to2. This pH may be obined by the addition of a concentrated strong acidsuch i HCl or HNO It has, however, been found advangeous to reach thedesired pH by addition of a metal .lt of a strong mineral acid such asHCl or HNO to :complish both the acidification and the further increaseconcentration of the composition with respect to the vetal oxide.

It should be noted that to broaden the range of com- )sitions in thefinal product, mixtures and particularly ixtures of the metal salts oforganic acids are found to a quite useful.

The fibering process comprises the following sequence 5 operations:

(1) Preparation of a suitable composition.

(2) Coating a clean glass substrate with a layer of the imposition ofthe proper thickness, between and 50 icrons being generally suitable.

(3) Removal of the liquid present by rapid heating to temperature ofabout 100 C. to 150 C. for a very [0111 time.

(4) Removal of the resulting fibers from the support- .g surface.

(5) Prefiring the fibers to remove all organic materials andsubstituents, 500 C. to 600 C. in a sagger being typical temperatures,and

(6) Final firing at about 1200 C. (900 C.l500 C. depending on thematerial processed and properties desired) for about one hour.

Once a solution is available for the production of fibers, a preferredfiber-forming procedure comprises pouring the solution onto a glasssurface in layer thicknesses of the order of 10 to 50 microns and thenplacing the same in the path of radiation of an infrared lamp. The fiberdimensions are determined in part by the thickness of the layer. If, asis preferred, the glass substrate is an absorber of infrared radiation,its temperature is raised almost immediately to a level of to 150 C.with the end result that the elimination of moisture and thefiberforming reaction itself are completed within a matter of one tofive minutes. The fibers thus obtained are loose since they break awayfrom the surface and produce a multiplicity of fibers ranging in lengthfrom 1 to 2 inches up to, in some cases, as long as 8 inches. The fibersare then placed in a sagger and given a prefire at temperatures between500 and 600 C. to remove all organic material and substituents, and arethen finally fired for periods of about one hour at temperatures of theorder of 1200 C.

The following specific examples will further illustrate the inventionand are to be regarded as illustrative of but a few of the many possiblevariations in materials, concentrations and procedures intended to beconstrued within the scope of the invention.

Example 1 The stock solutions from which the fibering matrix was madewere based on a zirconium acetate solution containing 15% zirconiumoxide by weight, concentrated hydrochloric acid containing 36% HCl byweight, a silica sol containing 35% silica by weight, and a trace ofwetting agent comprised of a 50% solution of sodium lauryl sulfonate.The reagents were placed in a beaker in the order hereinafter described,stirred, and immediately deposited on a clean glass surface.

Nine hundred and five cc. of the zirconium acetate solution were firstplaced in a glass beaker, followed by the addition of 44 cc. ofhydrochloric acid. Ten drops of the sodium lauryl sulfonate were thenadded, followed by 51 cc. of the 35% silica sol. As indicated, the reagents were added to the beaker in the order given and the batchvigorously stirred before the next reagent was added. Once the mixturewas available in fully stirred and fully mixed condition, it was thenpoured on infrared absorbing glass plates in thicknesses of between 10and 50 microns as established by doctor blading. The coated plates wereimmediately placed under a bank of infrared lamps having a total powerinput of 1500 watts which was focused on the glass plate supporting thefibering solution at a distance of 15 inches. Evaporation of solventcommenced substantially immediately and the fibering reaction wascompleted in approximately to seconds, as could be readily observedvisually since removal of the liquid resulted first in a cloudiness,then in a visible fracturing of the film, and the appearance ofneedle-like cracks in a generally parallel orientation. After the longslender fibers between 1 and 8 inches in length were formed on the glassplate, they were scraped off the surface with a silicone rubber bladeand then placed in a sagger and fired at 600 C. for one hour, afterwhich the sagger was removed from the furnace and placed in a secondfurnace at 1200 C. where the firing was continued for one hour longer,the sagger removed from the furnace, and the batch allowed to cool toroom temperature.

Chemical analysis of the fiber indicated that it contained approximately91% ZrO 8.3% silicon dioxide,

and the remainder consisted of traces of impurities such as alkalies,alkaline earths, iron oxide, and the like.

In comparing this fiber containing silica with a substantially purezirconium oxide fiber made in the same way and from the same compositionexcept for the absence of silica, it was found that the silicacontaining fibers exhibited tensile strength at room temperature in therange of 200,000 to 400,000 pounds per square inch, whereas the zirconiafibers made in the absence of silica exhibited tensile strengths in therange 50,000 to 100,000 pounds per square inch. After heat treatmentsfor six hours, at temperatures of 1750" C., the fibers produced in theabsence of silica became excessively brittle and crumpled readily ontouching, whereas the fibers containing the silica had not onlymaintained their original flexibility but gave evidence of actuallyhaving improved in tensile strength.

Fibers made and tested after the 1200 C. firing could be bent 90 throughabout ten cycles in the case of the zirconium oxide type before such afiber would fracture, whereas in the case of the zirconium oxide fiberscomplexed with silica, such fibers would stand at least 50 bends and insome cases up to 200 bends before fracturing was experienced.

Example 2 The same stock solutions as described in Example 1 wereutilized except that an added stock solution of zirconium oxychloride.was prepared by dissolving zirconium oxychloride crystals in water toproduce a 55% solution by weight of the octahydrate of zirconiumoxychloride in said water solution, equivalent to 21% zirconium oxide byweight.

As in Example 1, 900 cc. of the zirconium acetate solution were firstplaced in a beaker and added thereto was 77 cc. of the stock solution ofzirconium oxychloride. After vigorous stirring, drops of sodium laurylsulfonate were added, followed by the addition of 60 cc. of a 35% silicasol in water. The method as recited in Example 1 was followed yielding afiber containing approximately 91% zirconia and 8.5% silica. The fiberin raw form was produced on the glass plate about 60 to 70 seconds afterplacement under the infrared heaters.

Example 3 Two hundred twenty grams of commercial aluminum acetate wereadded to 850 cc. of water containing 60 cc. of concentrated hydrochloricacid. Twenty drops of sodium lauryl sulfonate were added and the batchstirred until a clear solution was obtained. Fifteen grams of 35 silicasol were then added and after vigorous stirring, the solution wassubject to the fibering and firing process described in Example 1. Theanalysis of the finished product showed 89.7% aluminum oxide, 9.5%silicon dioxide, and the balance consisting of minor amounts or tracesof impurities such as alkalies, iron oxide, lime, and the like. Fibersaveraging between 2 and 6 inches in length with thicknesses between 0.5and 0.2 micron and widths up to 5 microns were obtained.

Example 4 Ten cc. of concentrated hydrochloric acid were added to 500cc. of water. Fifty-five grams of hydrated ferric chloride crystals werestirred in until dissolved, followed by the addition of 200 grams ofhydrated ferrous acetate crystals. Twelve grams of 50% silica soldispersion in water were finally added and after vigorous stirring thesolution was subjected to the fibering and firing process described inExample 1. Fibers between 1 and 4 inches in length were obtained and inthe original drying process, fibers began to appear in 40 to 60 secondsafter placement under the infrared lights. The chemical analysis of thefinished fibers after firing indicated that they contained approximately93% iron oxide and approximately 7% silicon dioxide.

6 Example 5 Same as Example 4 except in place of the 200 grai of ferrousacetate ulilized in Example 4, a mixture of 1 grams of ferrous acetateand 100 grams of nickel aceti was used in the preparation. The finishedfiber had an ysis of approximately 45% nickel oxide, 48% iron oxi and 7%silicon dioxide, and was unusual in that it hibited a black lustrouscolor.

Example 6 Sixty grams of hydrated chromic chloride were d solved in 750:cc. of water, followed by the addition of 2 grams of hydrated chromousacetate. Twenty drops sodium lauryl sulfonate were added, followed by taddition of 18 grams of a 35% silica sol. Active fiberi action tookplace within about 60 seconds after inserti of a 20 micron thicksolution layer under the infrar lamps, and the finished fiber exhibiteda deep green c014 Analysis indicated that the fiber containedapproximate 91% chromium oxide and 8.5% silicon dioxide.

Having now described our invention in accordance wi the patent statutes,we claim:

1. A non-vitreous fiber in the form of a ribbon of r tangular crosssection composed of between about 5 and 15% by weight of silica andbetween about a 95% by weight of an oxide of a metal selected from tgroup consisting of aluminum, the rare earths, zirconiu: hafnium,thorium, iron, cobalt, manganese, nickel a: vanadium.

2. Fibers having a composition as defined in claim 1 a dimensions asfollows: lengths from about 1 inch up 8 inches, thicknesses between 0.1and 1.0 micron, a. widths from about 2 micron up to about 20 microns.

3. A fiber in the form of a ribbon of rectangular C1( section composedof a metal salt of a carboxylic ac whose dissociation constant isgreater than 1.5x 10 and silica; wherein the relative proportion ofmetallic s to silica when the metal salt is expressed as the equivalcmetallic oxide content in the metal salt, lie between to 95% metallicoxide and 5 to 15% silica, by weigl wherein the metal salts arecarboxylic acid salts of metal selected from the group consisting ofaluminu. the rare earths, zirconium, hafnium, thorium, iron, cobamanganese, nickel, and vanadium.

4. Fibers having a composition as defined in claim and dimensions asfollows: length from about 1 inch to 8 inches, thicknesses bet-ween 0.15and 1 /2 micro] and widths from about 2 microns up to about 30 micro] 5.A method of forming fibers in the form of ribbo of rectangular crosssection having a thickness from abc 0.1 micron to about 1 micron andwidths from abc 2 microns to about 20 microns and consisting of a majproportion of an oxide of a metal selected from the mo consisting ofaluminum, the rare earths, zirconiu hafnium, thorium, iron, cobalt,manganese, nickel a vanadium and a minor amount of silica which compriscpreparing a composition consisting essentially of a so tion containing(1) a metal salt of a carboxylic acid Wh( dissociation constant isgreater than 1.5 X 10- (2) a me salt of a strong mineral acid each ofsaid salts being salt of a metal selected from said group, and (3) asili sol; wherein the relative proportion of said metal sa to silicawhen expressed as oxides, lies between 85% 95 metallic oxide: 5%15%silica, by weight; formi a layer of the composition in a thickness up toabout microns, on an infrared absorbing support of a mater to which thefibers do not adhere; exposing the layer infrared to rapidly removesolvent therefrom, where the layer dries and disintegrates into fibers;and recov ing the loose fibers from the support.

6. The method of claim 5 wherein the pH of the fib forming compositionis adjusted to between 1 and 2 addition of a material from the groupconsisting of strc mineral acids and metallic salts of strong mineralaci 7. The method of claim 5 wherein the mineral acid is 2,013,857Kinzie Sept. 10, 1935 drochloric acid. 2,093,454 Kistler Sept. 21, 19378. The method of claim 5 wherein the carboxylic acid 2,491,761 ParkerDec. 20, 1949 acetic acid. 2,627,506 Hunter et al. Feb. 3, 1953 9. Themethod of claim 5 wherein the fibers are sub- 5 2,651,598 Ciapetta Sept.8, 1953 quently fired at between 500 C. and 600 C. to re- 2,808,338Bruno Oct. 1, 1957 ove all organic material and substituents and thenfired 2,886,404 Teja May 12, 1959 temperatures up to about 1200 C.2,915,475 Bugosh Dec. 1, 1959 2,917,426 Bugosh Dec. 15, 1959 ReferencesCited in the file of this patent UNITED STATES PATENTS .,577,189 PatrickMar. 16, 1926 10 2,934,443 Shell et a1 Apr. 26, 1960

1. A NON-VITREOUS FIBER IN THE FORM OF A RIBBON OF RECTANGULAR CROSSSECTION COMPOSED OF BETWEEN ABOUT 5% AND 15% BY WEIGHT OF SILICA ANDBETWEEN ABOUT 85% AND 95% BY WEIGHT OF AN OXIDE OF A METAL SELECTED FROMTHE GROUP CONSISTING OF ALUMINUM, THE RARE EARTHS, ZIRCONIUM, HAFNIUM,THORIUM, IRON, COBALT, MANGANESE, NICKEL AND VANADIUM.
 5. A METHOD OFFORMING FIBERS IN THE FORM OF RIBBONS OF RECTANGULAR CROSS SECTIONHAVING A THICKNESS FROM ABOUT 0.1 MICRON TO ABOUT 1 MICRON AND WIDTHSFROM ABOUT 2 MICRONS TO ABOUT 20 MICRONS AND CONSISTING OF A MAJORPROPORTION OF AN OXIDE OF A METAL SELECTED FROM THE GROUP CONSISTING OFALUMINUM, THE RARE EARTH, ZIRCONIUM, HAFNIUM, THORIUM, IRON, COBALT,MANGANESE, NICKEL AND VANADIUM AND A MINOR AMOUNT OF SILICA WHICHCOMPRISES: PREPARING A COMPOSITION CONSISTING ESSENTIALLY OF A SOLUTIONCONTAINING (1) A METAL SALT OF A CARBOXYLIC ACID WHOSE DISSOCIATIONCONSTANT IS GREATER THAN 1.5 X 10-5, (2) A METAL SALT OF A STRONGMINERAL ACID EACH OF SAID SALTS BEING A SALT OF A METAL SELECTED FROMSAID GROUP, AND (3) A SILICA SOL; WHEREIN THE RELATIVE PROPORTION OFSAID METAL SALTS TO SILICA WHEN EXPRESSED AS OXIDES, LIES BETWEEN 85% TO95% METALLIC OXIDE: 5%-15% SILICA, BY WEIGHT; FORMING A LAYER OF THECOMPOSITION IN A THICKNESS UP TO ABOUT 50 MICRONS, ON AN INFRAREDABSORBING SUPPORT OF A MATERIAL TO WHICH THE FIBERS DO NOT ADHERE;EXPOSING THE LAYER TO INFRARED TO RAPIDLY REMOVE SOLVENT THEREFROM,WHEREBY THE LAYER DRIES AND DISINTEGRATES INTO FIBERS; AND RECOVERINGTHE LOOSE FIBERS FROM THE SUPPORT.